1. Field of the invention
This invention relates to enamelling or painting plants in general and more specifically to plants of these type utilizing robot systems.
2. Description of the Prior Art
Generally, these plants are intended for enamelling or painting sanitary fittings, household electrical apparatuses and appliances, for example washing machines, refrigerators and so on. For namelling or painting such articles, present spray guns of an automatic type, are used in which the ceramic enamel or the paint to be handles is continuously fed to the spray gun through a feeder. In robotized installations the spray gun is mounted on an articulated wrist of a robot intended to perform all of the required and programmed working movements for a particular article to be enamelled or painted.
Present-day enamelling and painting plants comprise a feeder equipped with a diaphragm pump operated by compressed air. This diaphragm pump supplies enamel or paint from the feeder to the spray gun from which the enamel or paint is expelled outwardly by a jet of compressed air. Obviously, if robots are used to carry out the enamelling or painting operation, the spray gun is mounted on the wrist an arm of the robot which then performs all of the working movements programmed for the specific article to be enamelled or painted.
When very tall articles are to be enamelled or painted, the spray gun has to perform vertical movements of considerable extent with the spray gun operating at various working levels and thus at different working pressures. Since enamelling and painting operations generally utilize low pressures, of the order of about 0.5 atm. for reasons dictated by the enamel or paint characteristics, said difference in the working level or elevation will negatively affect the delivery flow rate of a spray gun because, with the pump delivery being constant, the pump will feed smaller amounts of enamel or paint at the highest levels than at the lowest levels, which results in an article being enamelled or painted in an uneven manner. By way of example, when bath tubs are to be enamelled which are about 2 m high, the spray gun has to perform a vertical movement of more than 2 m in order to enamel the border of the bath tub consequently, a pressure differential of more than 0.2 atm would exist between the lowest position and the highest position of the spray gun, which difference for an overall working pressure of 0.5 atm, is such as to undesirably affect the operation of the spray gun to a significant extent.